Power control of a robotic tool changer

ABSTRACT

A robotic tool changer removably attaches a robotic tool to a robotic arm. The changer includes a tool module connected to the robotic tool, and a master module connected to the robotic arm. To attach and detach the robotic tool, the changer couples and uncouples the tool module and the master module. A master electrical signal module (ESM) affixes to the master module and a tool ESM affixes to the tool module. In accordance with design requirements, the changer applies the same power supply to both the master ESM and the tool ESM. The changer, however, selectively suppresses application of the power supply to the tool ESM, while maintaining application of the power supply to the master ESM, during the coupling or uncoupling of the master module and the tool module. In doing so, the changer enables such coupling and uncoupling, while also preventing the formation of transient electric arcs.

This application claims is a continuation-in-part of U.S. patentapplication Ser. No. 12/699,687, filed Feb. 3, 2012, which claimspriority under 35 U.S.C. §119(e) from Provisional Patent Application No.61/149,932, filed Feb. 4, 2009, wherein the entire contents of each ofthese applications is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to the field of robotics and inparticular to power control of a robotic tool changer.

BACKGROUND

Robots are widely utilized in industrial assembly line and othermanufacturing applications to perform repetitive tasks very preciselywithout the need for human operation, interaction, or supervision. Forexample, robots are commonly used in the automotive industry to performa number of tasks such as material handling, cutting, welding, and thelike.

To amortize the considerable cost of an industrial robot over a varietyof tasks, the robot arm is typically separate from a diverse array ofrobotic tools, which are removably attached to the end of the robot arm.Different tools are removably attached in such a way through use of atool changer. The tool changer consists of a body for mechanicallyattaching the robot arm to a tool and one or more utility modulesconnected to that body for passing various utilities, such as electricalpower, between the robot arm and the tool. Specifically, one half of thetool changer body, called the master module, is permanently affixed tothe robot arm. The other half, called the tool module, is affixed toeach tool that the robot may utilize. When the robot arm positions themaster module adjacent the tool module connected to a desired tool, themaster module actuates a coupler to mechanically attach the master andtool modules together.

With the master and tool modules so attached, utility modules mayprovide for the passing of utilities between the robot and a tool. Forexample, a master electrical signal module may be affixed to the mastermodule and a tool electrical signal module may be affixed to the toolmodule. The master electrical signal module includes electrical contactsthat mate with those of the tool electrical signal module when themaster and tool modules are coupled together. With these electricalcontacts mated, electrical power is transferred from one or more powersupplies, across the master and tool electrical signal modules, and madeavailable at the tool.

Design restrictions of many tool changer applications dictate thatelectrical power transferred to the tool electrical signal module mustbe shared with the master electrical signal module (i.e., the masterelectrical signal module and the tool electrical signal module must usethe same one or more power supplies). Accordingly, because the masterelectrical signal module must provide electrical control signals to themaster module for actuating the coupler, the one or more power suppliesmust remain on during the coupling and uncoupling of the master and toolmodules. As a result, transient electric arcs form across the electricalcontacts of the master electrical signal module and the tool electricalsignal module during the coupling/uncoupling process. Especially whenhigh inrush current exists, arcing accelerates the wear of the contactsand thereby diminishes the contacts' electrical life below theirmechanical life.

Various methods are known to mitigate damage to the electrical contactscaused by arcing. Improving the material composition of the electricalcontacts, for example, permits the contacts to better withstand thestrain of arcing. These methods, however, merely prolong the electricallife of the contacts (e.g., to a point still short of their mechanicallife) because arcing still occurs.

SUMMARY

Methods and apparatus disclosed herein advantageously control the powerof a robotic tool changer to prevent arcing across the electricalcontacts of a master electrical signal module and a tool electricalsignal module. Instead of merely prolonging the electrical life of theelectrical contacts, the present invention allows the contacts to reachtheir mechanical life. The present invention also conforms to designrequirements of many tool changer applications by powering both themaster electrical signal module and the tool electrical signal modulewith the same one or more power supplies.

More particularly, the one or more power supplies apply power to themaster electrical signal module throughout a coupling and uncouplingprocess to permit the master module to actuate a coupler. A power switchcircuit, however, suppresses application of the one or more powersupplies to the tool electrical signal module throughout the couplingand uncoupling process to prevent arcing across the electrical contactsof the tool changer.

One embodiment of the present invention comprises, for example, poweringthe master electrical signal module via a first circuit connected to oneor more power supplies and powering the tool electrical signal modulevia a second circuit connected to the same one or more power suppliesthat is electrically parallel to the first circuit. The tool changerdetects a tool electrical signal module power control signal associatedwith the uncoupling of the master module and the tool module and,responsive thereto, breaks the second circuit while maintaining thefirst circuit. Because the tool changer maintains the first circuit, thetool changer may uncouple the master module and tool module (e.g., bythe master module actuating a coupler). During this uncoupling process,however, no arcing occurs across the electrical contacts because thetool changer has broken the second circuit and prevented the applicationof power to the tool electrical signal module. Thus, the tool changerallows the electrical contacts to reach their mechanical life.

Of course, the present invention is not limited to the above featuresand advantages. Indeed, those skilled in the art will recognizeadditional features and advantages upon reading the following detaileddescription, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a robotic tool changer of the present invention.

FIG. 2 is a block diagram illustrating one embodiment of a robotic toolchanger with the power control of the present invention.

FIGS. 3A and 3B are logic flow diagrams illustrating one or more methodsof controlling the power of a robotic tool changer.

FIG. 4 is a block diagram illustrating one embodiment of a robotic toolchanger with power control, exemplary power control signals, andcircuits for the protection of a power switch.

FIG. 5 is a block diagram illustrating an implementation of the robotictool changer of FIG. 4.

FIG. 6 is a block diagram illustrating one embodiment of a robotic toolchanger with alternative power control signals.

FIG. 7 is a block diagram illustrating one embodiment of a robotic toolchanger with yet other alternative power control signals.

FIG. 8 is a block diagram illustrating one embodiment of a robotic toolchanger with, again, alternative power control signals.

FIG. 9 is a block diagram illustrating an embodiment of a robotic toolchanger that is configured to removably attach a robotic tool to arobotic arm, and is also configured to removably dock the robotic toolwith a powered tool stand.

FIG. 10 is a block diagram illustrating an embodiment of a robotic toolchanger that is configured to removably dock a robotic tool with apowered tool stand.

FIG. 11 illustrates a high inrush current.

FIG. 12 illustrates one or more embodiments utilizing pulsed applicationof one or more power supplies.

FIGS. 13 and 14 illustrate the signal generator circuit's generation ofthe PWM control signal, as well as the resulting inrush current andoutput power going to the tool-side load.

FIG. 15 illustrates an example of a PWM control signal.

FIG. 16 illustrates further embodiments whereby the signal generatorcircuit is comprised within the power switch control circuit.

FIG. 17 is a diagram illustrating a process according to the presentinvention.

DETAILED DESCRIPTION

FIG. 1 depicts a robotic tool changer 10 according to one embodiment ofthe present invention. The robotic tool changer 10 comprises a mastermodule 12 adapted to be connected to a robotic arm (not shown) and atool module 14, adapted to be connected to a robotic tool (not shown).The robotic tool changer 10 allows users to selectively attach differenttools to a robotic arm by selectively coupling and uncoupling the mastermodule 12 and the tool module 14.

In the embodiment depicted in FIG. 1, alignment pins 16 on the mastermodule 12 are inserted into alignment holes 18 formed in the tool module14, to assist in achieving proper alignment between the master module 12and the tool module 14 during the coupling and uncoupling process. Theprocess of coupling the master and tool modules 12, 14 includesinserting a collar 48 protruding from the surface of the master module12 into a central chamber 46 formed in the tool module 14. The processof uncoupling the modules 12, 14 includes removing the collar 48 fromthe central chamber 46. In one embodiment, these processes are performedautomatically upon the master module receiving an electrical controlsignal directing it to couple or uncouple the modules 12, 14. Thoseskilled in the art will readily appreciate, however, that the couplingand uncoupling mechanisms shown are merely for illustrative purposes.Indeed, the present invention of power control is not limited by suchmechanisms.

Regardless of the specific coupling or uncoupling mechanisms, the toolchanger 10 provides for the passing of electrical power between one ormore power supplies and a robotic tool. For example, FIG. 1 depicts atool electrical signal module 20 affixed to the tool module 14. The toolelectrical signal module 20 includes tool-side electrical contacts 22connected internally to one or more connectors 24. A master electricalsignal module 26 is affixed to the master module 12. The masterelectrical signal module 26 includes robot-side electrical contacts 28adapted and disposed to mate with the tool-side electrical contacts 22when the master and tool modules 12, 14 are coupled together. Therobot-side electrical contacts 28 are connected internally to one ormore connectors 30. Electrical power may flow, for example, from one ormore power supplies (not shown) via connectors 30 and robot-sideelectrical contacts 28 to tool-side electrical contacts 22 andconnectors 24 when the master and tool modules 12, 14 are coupledtogether, and thence from connectors 24 to an attached tool (not shown).

Notably, the present invention controls this flow of electrical power toprevent arcing across the electrical contacts 28, 22 when the master andtool modules 12, 14 are being coupled and uncoupled (i.e., when theelectrical contacts 28, 22 of the master and tool electrical signalmodules 26, 20 are being mated and unmated). FIG. 2, for example,illustrates these electrical contacts 28, 22 and a power switch circuit58 for controlling the application of one or more power supplies 50 toan electrical load on a tool 52 via the modules 26, 20. The one or morepower supplies 50 may comprise, for example, two 24V DC power supplies.In conformance with the design requirements of many tool changerapplications, the one or more power supplies 50 are shared by both themaster and tool electrical signal modules 26, 20. The one or more powersupplies 50 apply power to the master electrical signal module 26throughout the coupling and uncoupling process. Such power permits themaster electrical signal module 26 to send an electrical control signalto the master module 12 directing it to actuate a coupler (e.g., thecollar 48 in FIG. 1). The power switch circuit 58, however, suppressesapplication of the one or more power supplies 50 to the tool electricalsignal module 20 throughout the coupling and uncoupling process toprevent arcing across the electrical contacts 28, 22.

More particularly, the one or more power supplies 50 power the masterelectrical signal module 26 via a first circuit 54 connected thereto.The one or more power supplies 50 also power the tool electrical signalmodule 20 via a second circuit 56 connected thereto that is electricallyparallel to the first circuit 54. (The second circuit 56 is electricallyparallel to the first circuit 54 so that breaking of either circuit 56,54 does not prevent the provision of power via the other). The powerswitch circuit 58 is disposed in series along the second circuit 56 inthe path of one or more poles of the circuit 56 (e.g., FIG. 2illustrates the power switch circuit 58 disposed in the path of thepositive pole, but it could also be disposed in the path of the negativepole).

Regardless of its specific disposition, the power switch circuit 58maintains the first circuit 54 connected between the one or more powersupplies 50 and the master electrical signal module 26 throughout thecoupling and uncoupling process, but breaks the second circuit 56connected between the one or more power supplies 50 and the toolelectrical signal module 20 during such a process. In doing so, thepower switch circuit 58 prevents arcing across the electrical contacts28, 22 when the master and tool modules 12, 14 are in the process ofbeing coupled and uncoupled. Accordingly, the power switch circuit 58allows the contacts 28, 22 to reach their mechanical life. The powerswitch circuit 58 also permits application of the one or more powersupplies 50 to the tool electrical signal module 20 when the master andtool modules 12, 14 have been coupled. That is, when the modules 12, 14have been coupled and are no longer in a transient state, the powerswitch circuit 58 establishes or re-establishes the second circuit 56.This allows for electrical operation of the tool attached to the toolmodule 12 once the modules 12, 14 have been coupled together.

To apply and suppress the application of the one or more power supplies50 in this manner, the power switch circuit 58 is controlled by a powerswitch control circuit 60. The power switch control circuit 60 directsthe power switch circuit 58 to break the second circuit 56 during thecoupling and uncoupling process and to establish or re-establish thesecond circuit 56 at other times (e.g., when the master and tool modules12, 14 have been coupled). Specifically, the power switch controlcircuit 60 receives one or more tool electrical signal module powercontrol signals 62 that are associated with the coupling and uncouplingprocess. These one or more signals 62 indicate to the power switchcontrol circuit 60 that the coupling and uncoupling process is occurringor is about to occur. Responsive to the one or more signals 62, thepower switch control circuit 60 directs the power switch circuit 58 tobreak or establish the second circuit 56 connected between the one ormore power supplies 50 and the tool electrical signal module 20.

With the above points of variation and implementation of the robotictool changer 10 in mind, those skilled in the art will appreciate thatthe tool changer 10 of the present invention generally performs themethod illustrated in FIGS. 3A (uncoupling) and 3B (coupling). Accordingto FIG. 3A, the robotic tool changer 10 powers the master electricalsignal module 26 via a first circuit 54 connected to the one or morepower supplies 50 (Block 100) while powering the tool electrical signalmodule 20 via a second circuit 56 connected to the same one or morepower supplies 50 (Block 110). The second circuit 56 is electricallyparallel to the first circuit 54 so that breaking of the second circuit56 does not prevent the provision of power via the first circuit 54. Todiscriminate when to break the second circuit 56, however, the toolchanger 10 receives one or more tool electrical signal module powercontrol signals 62 associated with the uncoupling of the master module12 and the tool module 14 (Block 120). Responsive to these one or moretool electrical signal module power control signals 62, the tool changer10 (via the power switch circuit 58) breaks the second circuit 56connected between the one or more power supplies 50 and the toolelectrical signal module 20 (Block 130). Because the tool changer 10maintains the first circuit 54 connected between the one or more powersupplies 50 and the master electrical signal module 26, the tool changer10 may uncouple the master module 12 and tool module 14 (e.g., by themaster module 12 actuating a coupler) (Block 140). During thisuncoupling process, however, no arcing occurs across electrical contacts28, 22 because the tool changer 10 has broken the second circuit 56 andprevented the application of power to the tool electrical signal module20. Thus, tool changer 10 allows the contacts 28, 22 to reach theirmechanical life.

Those skilled in the art will readily appreciate, of course, that themethod illustrated in FIG. 3A may be performed as part of an ongoingprocess and may be implemented in conjunction with or independently fromthe steps illustrated in FIG. 3B. After uncoupling the master module 12and the tool module 14, for example, the robotic arm may be configuredto perform a task with a different tool. To do so, the master module 12must be coupled to a tool module 14 connected to the different tool. Oneembodiment of the present invention, therefore, includes the robotictool changer 10 maintaining the first circuit 54 and keeping the secondcircuit 56 broken while the master module 12 and the tool module 14 areuncoupled.

Regardless of the status of the second circuit 56 during such time,however, the method may continue according to the steps illustrated inFIG. 3B. In FIG. 3B, when the master module and the tool module arebeing coupled together (Block 150), the second circuit 56 is or remainsbroken so that no arcing occurs across the electrical contacts 28, 22.The robotic tool changer 10 receives one or more tool electrical signalmodule power control signals 62 associated with this coupling (Block160), such as an indication that the modules 12, 14 have been coupledtogether. Responsive thereto, the robotic tool changer 10 (via the powerswitch circuit 58) re-establishes the second circuit 56 connectedbetween the one or more power supplies 50 and the tool electrical signalmodule 20 (Block 170).

Of course, while the methods illustrated in FIGS. 3A and 3B have beendescribed together in the order of uncoupling followed by coupling,those skilled in the art will appreciate that these methods may beperformed together or independently and without regard to such order.Nor is the present invention limited by the manner in which these stepsare performed. Indeed, FIG. 4 illustrates one embodiment of the robotictool changer 10 performing the above-described method through use ofspecific tool electrical signal module power control signals 62.

In FIG. 4, the tool electrical signal module power control signals 62comprise three separate signals, namely an ON/OFF signal 63, a LOCKEDsignal 64, and one or more READY TO LOCK signals 65. The ON/OFF signal63 represents an explicit control command to the power switch controlcircuit 60 to either turn power on to the tool electrical signal module20 (i.e., establish the second circuit 56) or turn power off to the toolelectrical signal module 20 (i.e. break the second circuit 56). In oneembodiment, for example, a controller of the robot sends an OFF commandto the robotic tool changer 10 shortly before commanding the toolchanger 10 to uncouple the modules 12, 14. Likewise, the controllersends an ON command to the robotic tool changer 10 shortly aftercommanding the tool changer 10 to couple the modules 12, 14.

The one or more READY TO LOCK signals 65 and the LOCKED signal 64 eachrepresent a sensing signal that indicates a different stage ofuncoupling or coupling of the modules 12, 14. The one or more READY TOLOCK signals 65, for example, indicate that the master and tool modules12, 14 are close enough for mechanical attachment. The LOCKED signal 64indicates the modules 12, 14 are sensed as being locked in place via alocking mechanism. These sensing signals 64, 65 are merely illustrative,of course, as the power switch control circuit 60 may be configured torespond to any number or type of sensing signals indicative of thestatus of uncoupling or coupling of the modules 12, 14. Regardless ofthe particular sensing signal, therefore, the power switch controlcircuit 60 may direct the power switch circuit 58 to break or establishthe second circuit 56 at any one of a number of stages of the uncouplingor coupling process, respectively.

FIG. 4 also illustrates one embodiment of the robotic tool changer 10that includes a current limiting circuit 66 and a voltage limitingcircuit 68. The current limiting circuit 66, for example, protects thepower switch circuit 58 from overload due to high inrush current. Thevoltage limiting circuit 68 protects the power switch circuit 58 fromvoltage spikes caused by inductive electrical loads 52. These protectioncircuits 66, 68, therefore, allow the present invention to utilizecertain power switch circuits 58 despite their inability to sustain agiven inrush current or voltage spike. Accordingly, as embodiments ofthe present invention may alternatively utilize a power switch circuit58 capable of sustaining such high inrush current or voltage spikes,embodiments of the present invention are not limited by the presence ofthese circuits 66, 68. Nor are embodiments of the present inventionlimited by the implementation of these, or any other, circuits.

FIG. 5 shows one embodiment of the robotic tool changer 10 according tothe present invention. The power switch control circuit 60 comprises atwo input AND logic gate LG₁ having one READY TO LOCK signal 65 and theLOCKED signal 64 as inputs. The power switch control circuit 60 alsocomprises a two input OR logic gate LG₂ having the result of LG₁ and theON/OFF signal 63 as inputs. As illustrated, therefore, the power switchcircuit 58 is controlled by the power switch control circuit 60responsive to either the ON/OFF signal 63 alone OR the combination ofthe READY TO LOCK signal 65 AND the LOCKED signal 64.

FIG. 5 illustrates the power switch circuit 58 implemented as atransistor M₁. The transistor M₁ establishes the second circuit 56connected between the one or more power supplies 50 and the toolelectrical signal module 20 when the output from the power switchcontrol circuit 60 is logically high. This occurs, for instance, wheneither the ON/OFF signal 63 is high (indicating an explicit controlcommand that the circuit 56 should be established) OR the READY TO LOCKsignal 65 AND the LOCKED signal 64 are both high (sensing that themodules 12, 14 are physically close and have been locked together). Bycontrast, the transistor M₁ breaks the second circuit 56 when the outputfrom the power switch control circuit 60 is logically low. This occurswhen either the ON/OFF signal 63 is low (indicating an explicit controlcommand that the circuit 56 should be broken) OR at least one of theREADY TO LOCK signal 65 AND the LOCKED signal 64 are low (sensing thatthe modules 12, 14 either are not physically close or have not beenlocked together).

During the establishment or breaking of the second circuit 56, however,inrush current or voltage spikes may threaten the transistor M₁. Toprevent such damage, FIG. 5 illustrates an exemplary current limitingcircuit 66 and voltage limiting circuit 68. The current limiting circuit66 includes a transistor Q₁ controlled by the network of passivecomponents R₁, R₂, and R₃ to actively regulate the current passingthrough M₁. The voltage limiting circuit 68 includes two opposing zenerdiodes D₁ and D₂ configured to clip voltage spikes above or below theoperating voltage level of the robotic tool changer 10. With thetransistor M₁ protected from such inrush current and voltage spikes, thetransistor M₁ need not be capable of sustaining high levels thereof.

FIGS. 6-8 illustrate yet other embodiments of the robotic tool changer10 that include different tool electrical signal module power controlsignals 62. FIG. 6 illustrates an embodiment whereby the tool electricalsignal module power control signals 62 comprise only the LOCKED signal64. In this case, the power switch circuit 58 is controlled responsiveonly to whether the LOCKED signal 64 is logically high or low. (Notethat the power switch control circuit 60 is not shown in FIG. 6 becausein this embodiment it simply acts as a buffer to isolate the powerswitch circuit 58 and to otherwise relay the logic high or low of theLOCKED signal 64 to the power switch circuit 58). The power switchcircuit 58, therefore, breaks the second circuit 56 when the modules 12,14 have not been locked together, and re-establishes the second circuit56 when the modules 12, 14 have been locked together.

While the embodiment in FIG. 6 certainly prevents arcing across theelectrical contacts 28, 22, it nonetheless appreciably delaysapplication of power to the robotic tool longer than absolutelynecessary to prevent such arcing. More particularly, once the modules12, 14 are physically close, as indicated by the READY TO LOCK signal65, a controller of the robot (not shown) sends a LOCK command signal tothe tool changer 10 directing it to actuate a locking mechanism to lockthe modules 12, 14 together. At some point between the locking mechanisminitiating and the modules 12, 14 actually locking together, all of theelectrical contacts 28, 22 engage. With all of the electrical contacts28, 22 engaged, it is at this point when the second circuit 56 could bere-established and power applied to the robotic tool without causingarcing across the electrical contacts 28, 22. The embodiment in FIG. 6,however, delays re-establishing the second circuit 56 and application ofpower to the robotic tool until some appreciable time after this point(e.g., 100 ms), when the LOCKED signal 64 indicates that the modules 12,14 have actually been locked together.

FIGS. 7 and 8 illustrate alternative embodiments that minimize thisdelay. In FIG. 7, the tool electrical signal module power controlsignals 62 comprise the READY TO LOCK signal 65. The READY TO LOCKsignal 65 becomes logically high once the modules 12, 14 are physicallyclose, which may occur before all of the electrical contacts 28, 22 areengaged (and thereby before power can be applied to the robotic toolwithout causing arcing across the electrical contacts 28, 22). However,the READY TO LOCK signal 65 first passes through a connector 80B,through a circuit path in the tool electrical signal module 20, and thenthrough a physically recessed electrical contact 80A before being inputinto the power switch circuit 58 (or the power switch control circuit60, since just as in FIG. 6, the power switch control circuit 60 simplyacts as a buffer to isolate the power switch circuit 58 and to otherwiserelay the logic high or low of the READY TO LOCK signal 65, once passedthrough the physically recessed electrical contact 80A, to the powerswitch circuit 58). Because the electrical contact 80A is physicallyrecessed, it is the last of the electrical contacts to engage. Oncepassed through the physically recessed electrical contact 80A,therefore, the READY TO LOCK signal 65 indicates both whether themodules 12, 14 are physically close and whether all electrical contacts28, 22 are engaged. Accordingly, the power switch circuit 58 in FIG. 7re-establishes the second circuit 56 as soon as the modules 12, 14 arephysically close and all electrical contacts 28, 22 are engaged.Likewise, the power switch circuit 58 breaks the second circuit 56 wheneither the modules 12, 14 are not physically close, or the physicallyrecessed electrical contact 80A is not longer engaged.

In FIG. 8, the tool electrical signal module power control signals 62comprise a LOCK command signal 70, a corresponding UNLOCK command signal72, and a TOOL PRESENT signal 74. A controller of the robot sends theLOCK command signal 70 to a tool changer control circuit 76 included inthe tool changer 10. Responsive to the LOCK command signal 70 beinglogically high, the tool changer control circuit 76 directs the mastermodule 12 to actuate a locking mechanism to lock the modules 12, 14together. The power switch control circuit 60, included in the toolchanger control circuit 76 in this embodiment, also receives the LOCKcommand signal 70, but does not yet direct the power switch circuit 58to re-establish the second circuit 56. Rather, the power switch controlcircuit 60 waits until both the LOCK command signal 70 and the TOOLPRESENT signal 74 are logically high. The TOOL PRESENT signal 74 is asensing signal that is passed from the power switch control circuit 60,through a physically recessed electrical contact 80A, through a circuitpath in the tool electrical signal module 20, and then through anelectrical contact 80B back to the power switch control circuit 60.Passed through the physically recessed electrical contact 80A, the TOOLPRESENT signal 74 indicates whether all of the electrical contacts 28,22 are engaged. Accordingly, the power switch control circuit 60 directsthe power switch circuit 58 to re-establish the second circuit 56 assoon as the command has been given to lock the module 12, 14 togetherand all electrical contacts 28, 22 are engaged.

Similarly, the controller of the robot sends the UNLOCK command signal72 to the tool changer control circuit 76. Responsive to the UNLOCKcommand signal 72 being logically high, the tool changer control circuit76 directs the master module 12 to actuate the locking mechanism tounlock the modules 12, 14. The power switch control circuit 60 alsoreceives the UNLOCK command signal 72. As soon as the power switchcontrol circuit 60 receives the UNLOCK command signal 72 (i.e., whileall electrical contacts 28, 22 are still engaged), it directs the powerswitch circuit 58 to break the second circuit 56.

FIG. 9 illustrates other embodiments of the robotic tool changer 10. Thetool changer 10 in these embodiments includes a first master module 12that is connected to a first powered endpoint 81 (shown in the exampleof FIG. 9 as robotic arm 81), and a first tool module 14 that isconnected to robotic tool 82. The tool changer 10 removably attaches therobotic tool 82 to the first powered endpoint 81, by coupling anduncoupling the first master module 12 and the first tool module 14 inmuch the same way as described above. When coupled, the tool changer 10applies electrical power from the power supply 50 to the tool 82.Electrical power flows, for example, from the power supply 50 to a firstmaster electrical signal module 26 affixed to the first master module12, from endpoint-side electrical contacts 28 to tool-side electricalcontacts 22, and then from a first tool electrical signal module 20affixed to the first tool module 14 to the tool 82. Similar to theembodiments described above, the tool changer 10 prevents transientelectric arcs from forming across electrical contacts 28, 22 bysuppressing application of the power supply 50 to the first toolelectrical signal module during the coupling or uncoupling of the firstmaster module 12 and the first tool module 14.

The tool changer 10 in FIG. 9, however, is also configured to transferthe robotic tool 82 between the first powered endpoint 81 (i.e., roboticarm 81) and a second powered endpoint 83 (shown in the example of FIG. 9as powered tool stand 83). When the robotic tool 82 is transferred tothe second powered endpoint 83, the endpoint 83 powers the robotic tool82 by applying the one or more power supplies 50 to the tool 82. In FIG.9, for example, the powered tool stand 83 powers the robotic tool 82with power from the power supply 50, when the tool 82 is docked with thestand 83.

Accordingly, the tool changer 10 in FIG. 9 further includes a secondtool module 84 that is connected to the robotic tool 82, and a secondmaster module 85 that is connected to the second powered endpoint 83(i.e., the powered tool stand 83). The second master module 85 isconfigured to couple to and uncouple from the second tool module 84 inmuch the same way as described above with respect to the first mastermodule 12 and the first tool module 14. To transfer the tool 82 betweenthe first powered endpoint 81 and the second powered endpoint 83,therefore, the tool changer 10 coordinates the coupling and uncouplingof the first master module 12 and the first tool module 14 with thecoupling and uncoupling of the second master module 85 and the secondtool module 84. In one embodiment, for example, the tool changer 10transfers the robotic tool 82 from the first powered endpoint 81 to thesecond powered endpoint 83 by coupling the second master module 85 andthe second tool module 84 and then, shortly thereafter, uncoupling thefirst master module 12 and the first tool module 14. Such coordinationmay entail coupling and uncoupling the second master module 85 and thesecond tool module 84 responsive to tool electric signal module powercontrol signals 90 that are the same as the control signals 62 discussedabove.

To transfer power from the power supply 50 to the tool 82 via the secondpowered endpoint 83, the tool changer 10 further includes a secondmaster electrical signal module 87 affixed to the second master module85 and a second tool electrical signal module 86 affixed to the secondtool module 84. The second master electrical signal module 87 includesendpoint-side electrical contacts 88 adapted and disposed to mate withthe tool-side electrical contacts 89 when the second master and toolmodules 84, 85 are coupled together. To prevent transient electric arcsfrom forming across these contacts 88, 89, the tool changer 10selectively suppresses application of the one or more power supplies 50to the second tool electrical signal module 86 during the coupling anduncoupling of the second master and tool modules 84, 85. In doing so,however, the tool changer 10 maintains application of the one or morepower supplies 50 to the second master electrical signal module 87, toenable the coupling and uncoupling of the second master and tool modules84, 85 in the first place.

FIG. 10 illustrates additional details of the second master and toolelectrical signal modules 86, 87 according to one embodiment. The one ormore power supplies 50 power the second master electrical signal module87 via a third circuit 91 connected thereto. The one or more powersupplies 50 also power the second tool electrical signal module 86 via afourth circuit 92 connected thereto that is electrically parallel to thethird circuit 91. (The first and second circuits 54, 56 being thosedescribed for powering the first master and tool electrical signalmodules 12, 14). A second power switch circuit 93 is disposed in seriesalong the fourth circuit 92 in the path of one or more poles of thecircuit 92. The second power switch circuit 93 is configured toselectively break or establish the fourth circuit 92, while maintainingthe third circuit 91, in much the same way as described above withrespect to other embodiments. For example, the second power switchcircuit 93 in one embodiment is controlled by the second power switchcontrol circuit 94. The second power switch control circuit 94 directsthe second power switch circuit 93 to break or establish the fourthcircuit 92 responsive to one or more second tool electrical signalmodule power control signals 90 (which may or may not be the same as thecontrol signals 62 described above). Regardless, such prevents arcingacross the electrical contacts 88, 89 when the second master and toolmodules 86, 87 are in the process of being coupled and uncoupled.Accordingly, the second power switch circuit 93 allows the contacts 88,89 to reach their mechanical life, while at the same time enabling thecoupling and uncoupling of the modules 86, 87.

FIGS. 9 and 10 illustrated embodiments of the tool changer 10 using thetransfer of a robotic tool 82 between a robotic arm, as one example of afirst powered endpoint 81, and a powered tool stand as one example of asecond powered endpoint 83. In some embodiments, however, the first andsecond powered endpoints 81, 83 comprise other types of endpoints thatpower the robotic tool 82.

In one embodiment, for example, the tool changer 10 transfers therobotic tool 82 between a robotic arm 81 and a powered transport, asanother type of powered endpoint 83. A powered transport as used hereinrefers to any type of mechanical vehicle or the like that physicallytransports the robotic tool 82 (e.g., from one location to another), andthat powers the robotic tool 82 during such transport. In yet otherembodiments, the tool changer 10 transfers the robotic tool 82 between apowered transport and a powered tool stand. Over various embodiments,therefore, the tool changer 10 may be configured to transfer the robotictool 10 from a powered tool stand to a powered transport, from thepowered transport to a robotic arm, and vice versa, while preventingtransient electric arcs from forming during each transfer.

In yet other embodiments, though, the tool changer 10 may simply beconfigured to removably attach the robotic tool 82 to any one poweredendpoint (i.e., without regard to transferring the robotic tool 82between that endpoint and another powered endpoint). For example, thetool changer 10 may simply be configured to removably attach the robotictool 82 to the robotic arm 81, as described in earlier embodiments.Alternatively, the tool changer 10 may be configured to removably attachthe robotic tool 82 to a powered tool stand, or a powered transport.

Embodiments described above prove advantageous for most applications.Some applications, however, push the limits of the embodiments' abilityto protect the one or more power supplies 50 from glitching due to highinrush current. The high inrush current 204 shown in FIG. 11, forinstance, likely exceeds 50 A, though the current probe used was limitedto 27 A. Especially where the one or more power supplies 50 are only ofmarginal quality, such a high inrush current threatens to cause thepower level provided by the one or more power supplies 50 to drop.

One or more embodiments herein advantageously address these problemsthrough pulsed application of the one or more power supplies 50 uponmodule coupling. More specifically, according to some embodiments, thepower switch circuit 58 administers pulsed application of the one ormore power supplies 50 upon coupling of the first master module 12 andthe first tool module 14. Administering pulsed application in this waytransitions the power switch circuit 58 from suppressing application ofthe one or more power supplies 50 to the first tool electrical signalmodule 20, to maintaining application of the one or more power supplies50 to the first tool electrical signal module 20. Pulsed application inthis regard refers to power supply application that occurs in pulses,where the pulses may be configured in frequency, width, duty cycle, andthe like as needed.

FIG. 12 illustrates one or more embodiments in this regard. As shown inFIG. 12, the power switch circuit 58 is configured to administer pulsedapplication of the one or more power supplies 50 responsive to apulse-width modulated (PWM) control signal 200. This signal 200 isassociated with coupling of the first master module 12 and the firsttool module 14. In some embodiments, for instance, the signal 200comprises an explicit control command that indicates whether to turnpower on or off to the first tool electrical signal module 20 (i.e., thesignal 200 comprises the ON/OFF signal 63).

As shown in FIG. 12, the tool changer 10 includes a signal generatorcircuit 202 that is configured to generate this PWM control signal 200.The signal generator circuit 202 in some embodiments is configured togenerate the PWM control signal 200 to meet one or more performancecriteria with regard to the signal 200, the inrush current, and/or thepowering of the tool changer 10.

In at least one embodiment, for instance, the signal generator circuit202 is configured to generate the PWM control signal 200 based ontransitioning from suppressing application to maintaining application ofthe one or more power supplies 50 to the first tool electrical signalmodule 20 within a defined time period. Consider FIGS. 13 and 14. Thesegraphs illustrate the signal generator circuit's 202 generation of thePWM control signal 200, as well as the resulting inrush current 204 andoutput power 206 going to the tool-side load. As shown in FIGS. 13 and14, the signal generator circuit's 202 generation of the PWM controlsignal 200 to have a width of 50 μs and a frequency of 1 kHz turns thepower on to the tool-side load fairly quickly. However, at the sametime, an inrush current 204 of about 12 Amps results.

In one or more other embodiments, therefore, the signal generatorcircuit 202 is configured to generate the PWM control signal 200 basedon limiting the current passing through the first power switch circuit58 to be at or below a defined inrush current. FIG. 15 illustrates oneexample. As shown in FIG. 15, the signal generator circuit's 202generation of the PWM control signal 200 to have a width of 25 μs and afrequency of 1 kHz limits the inrush current 204 to about 5 Amps ratherthan 12 Amps. One competing consideration, though, is that the powerdoes not turn on to the tool-side load as quickly.

From these examples, one skilled in the art thus appreciates that thesignal generator circuit 202 is configured in some embodiments togenerate the signal 200 with some combination of frequency and pulsewidth that yields desired performance characteristics. The circuit 202may also dynamically adjust the signal's parameters to yield thosecharacteristics, such as by increasing the frequency and graduallyincreasing the pulse width as desired.

Similarly, the signal generator circuit 202 in at least some embodimentsis configured to dynamically adjust one or more parameters of the PWMcontrol signal 200 based on feedback 208 indicative of an electricalload on the robotic tool 52. FIG. 12, for instance, illustrates anexample feedback point (A) that indicates the electrical load on thetool 52, e.g., in terms of output voltage.

FIG. 16 illustrates still other embodiments whereby the signal generatorcircuit 202 is comprised within the power switch control circuit 60. Inthis case, the power switch control circuit 60 operates substantiallythe same as described above, in terms of controlling the power switchcircuit 58 based on the LOCK 70, UNLOCK 72, and TOOL PRESENT 74 signals,and or other tool electrical signal module power control signals 62associated with the coupling of the first master module 12 and the firsttool module 14.

However, the control circuit 60 is configured to direct the power switchcircuit 58 to administer pulsed application of the power suppl(ies) 50responsive to the PWM control signal 200 under certain conditions. Theseconditions may be defined, for instance, in terms of a control commandto lock the first master module 12 and the first tool module 14 (i.e.,the LOCK signal 70), and a sensing signal that indicates whether allelectrical contacts between the first master module 12 and the firsttool module 14 are engaged (i.e., the TOOL PRESENT signal 74). In thiscase, the signals 70, 74 would indicate that the modules 12, 14 arecoupled, meaning that the power switch control circuit 60 would directthe power switch circuit 58 to apply the one or more power supplies 50to the tool electrical signal module 20. But rather than directing thepower switch circuit 58 to immediately switch from suppressingapplication of the power supplies 50 to fully maintaining application ofthe power supplies 50, the control circuit 60 directs the power switchcircuit 58 to administer pulsed application of the power supplies 50 toyield a (e.g., smooth and fairly gradual) transition between applicationsuppression and application maintenance. Accordingly, the controlcircuit 60 directs the signal generator circuit 202 to generate the PWMcontrol signal 200 and apply that signal to the power switch circuit 58for pulsed power application.

Although not explicitly shown in the context of all previous FIGS. 1-10,pulsed power application may be employed in those embodiments as well.This includes an analogous use of pulsed power application for thesecond master electrical signal module 87 and the second tool electricalsignal module 86 in FIG. 10.

Accordingly, those skilled in the art will appreciate that a robotictool changer 10 herein generally performs the processing shown in FIG.17. As shown in FIG. 17, processing includes applying one or more powersupplies to both a first master electrical signal module, affixed to thefirst master module, and a first tool electrical signal module, affixedto the first tool module (Block 300). Processing further includes,during the coupling or uncoupling of the first master module and thefirst tool module, selectively suppressing application of the one ormore power supplies to the first tool electrical signal module, whilemaintaining application of the one or more power supplies to the firstmaster electrical signal module (Block 310). Finally, processingincludes, upon coupling of the first master module and the first toolmodule, administering pulsed application of the one or more powersupplies to the first tool electrical signal module to transition fromsuppressing application to maintaining application of the one or morepower supplies to the first tool electrical signal module (Block 320).

It should be understood, therefore, that the foregoing description andthe accompanying drawings represent non-limiting examples of the methodsand individual apparatuses taught herein. As such, the present inventionis not limited by the foregoing description and accompanying drawings.Instead, the present invention is limited only by the following claimsand their legal equivalents.

What is claimed is:
 1. A robotic tool changer system configured toremovably attach a robotic tool to a robotic arm, comprising: a firsttool module adapted to be connected to the robotic tool; a first mastermodule adapted to be connected to the robotic arm, and to selectivelycouple to and uncouple from the first tool module; a first masterelectrical signal module affixed to the first master module and a firsttool electrical signal module affixed to the first tool module, bothadapted to be powered by application of the same one or more powersupplies; and a first power switch circuit configured to: selectivelysuppress application of the one or more power supplies to the first toolelectrical signal module, while maintaining application of the one ormore power supplies to the first master electrical signal module, duringthe coupling or uncoupling of the first master module and the first toolmodule; and upon coupling of the first master module and the first toolmodule, administer pulsed application of the one or more power suppliesto the first tool electrical signal module to transition fromsuppressing application to maintaining application of the one or morepower supplies to the first tool electrical signal module.
 2. Therobotic tool changer system of claim 1, wherein the first power switchcircuit is configured to administer said pulsed application responsiveto a pulse-width modulated control signal that is associated withcoupling of the first master module and the first tool module.
 3. Therobotic tool changer system of claim 2, wherein the pulse-widthmodulated control signal comprises an explicit control command thatindicates whether to turn power on or off to the first tool electricalsignal module.
 4. The robotic tool changer system of claim 2, furthercomprising a signal generator circuit configured to generate thepulse-width modulated control signal.
 5. The robotic tool changer systemof claim 4, wherein the signal generator circuit is configured togenerate the pulse-width modulated control signal based on transitioningfrom suppressing application to maintaining application of the one ormore power supplies to the first tool electrical signal module within adefined time period.
 6. The robotic tool changer system of claim 4,wherein the signal generator circuit is configured to generate thepulse-width modulated control signal based on limiting the currentpassing through the first power switch circuit to be at or below adefined inrush current.
 7. The robotic tool changer system of claim 4,wherein the signal generator circuit is configured to dynamically adjustone or more parameters of the pulse-width modulated control signal basedon feedback indicative of an electrical load on the robotic tool.
 8. Therobotic tool changer system of claim 4, wherein the signal generatorcircuit is configured to generate the pulse-width modulated controlsignal responsive to one or more first tool electrical signal modulepower control signals associated with the coupling of the first mastermodule and the first tool module.
 9. The robotic tool changer system ofclaim 8, wherein the one or more first tool electrical signal modulepower control signals comprise a control command to lock the firstmaster module and the first tool module, and a sensing signal thatindicates whether all electrical contacts between the first mastermodule and the first tool module are engaged.
 10. The robotic toolchanger system of claim 2, further comprising a first power switchcontrol circuit configured to direct the first power switch circuit toadminister said pulsed application responsive to the pulse-widthmodulated control signal.
 11. The robotic tool changer system of claim1, wherein the first master electrical signal module is powered via afirst circuit connected to the one or more power supplies and the firsttool electrical signal module is powered via a second circuit connectedto the one or more power supplies that is electrically parallel to thefirst circuit, and wherein the first power switch circuit is configuredto selectively break or establish the second circuit, while maintainingthe first circuit.
 12. The robotic tool changer system of claim 1,wherein the first master electrical signal module and the first toolelectrical signal module include robot-side electrical contacts andtool-side electrical contacts, respectively, that are adapted anddisposed to mate with one another and to pass electrical powertherebetween when the first master module and the first tool module arecoupled together, and wherein the first power switch circuit isconfigured to: prevent transient electric arcs from forming across saidrobot side and said tool-side electrical contacts by suppressingapplication of the one or more power supplies to the first toolelectrical signal module during the coupling or uncoupling of the firstmaster module and the first tool module; and enable the coupling oruncoupling of the first master module and the first tool module bymaintaining application of the one or more power supplies to the firstmaster electrical signal module.
 13. The robotic tool changer system ofclaim 1, wherein the robotic tool changer system is further configuredto transfer the robotic tool between the robotic arm and a poweredendpoint, the robotic tool changer system further comprising: a secondtool module adapted to also be connected to the robotic tool; a secondmaster module adapted to be connected to said powered endpoint, and toselectively couple to and uncouple from the second tool module incoordination with the coupling and uncoupling of the first master moduleand the first tool module; a second master electrical signal moduleaffixed to the second master module and a second tool electrical signalmodule affixed to the second tool module, both adapted to be powered byapplication of the one or more power supplies; and a second power switchcircuit configured to: selectively suppress application of the one ormore power supplies to the second tool electrical signal module, whilemaintaining application of the one or more power supplies to the secondmaster electrical signal module, during the coupling or uncoupling ofthe second master module and the second tool module; and upon couplingof the second master module and the second tool module, administeringpulsed application of the one or more power supplies to the second toolelectrical signal module to transition from suppressing application tomaintaining application of the one or more power supplies to the secondtool electrical signal module.
 14. A method implemented by a robotictool changer system for removably attaching a robotic tool to a roboticarm by selectively coupling and uncoupling a first tool module connectedto the robotic tool and a first master module connected to the roboticarm, the method comprising: applying the same one or more power suppliesto power both a first master electrical signal module, affixed to thefirst master module, and a first tool electrical signal module, affixedto the first tool module; during the coupling or uncoupling of the firstmaster module and the first tool module, a power switch circuit of therobotic tool changer system selectively suppressing application of theone or more power supplies to the first tool electrical signal module,while maintaining application of the one or more power supplies to thefirst master electrical signal module; and upon coupling of the firstmaster module and the first tool module, the power switch circuitadministering pulsed application of the one or more power supplies tothe first tool electrical signal module to transition from suppressingapplication to maintaining application of the one or more power suppliesto the first tool electrical signal module.
 15. The method of claim 14,wherein said administering comprises administering said pulsedapplication responsive to a pulse-width modulated control signal that isassociated with coupling of the first master module and the first toolmodule.
 16. The method of claim 15, wherein the pulse-width modulatedcontrol signal comprises an explicit control command that indicateswhether to turn power on or off to the first tool electrical signalmodule.
 17. The method of claim 15, further comprising generating thepulse-width modulated control signal.
 18. The method of claim 17,wherein said generating comprises generating the pulse-width modulatedcontrol signal based on transitioning from suppressing application tomaintaining application of the one or more power supplies to the firsttool electrical signal module within a defined time period.
 19. Themethod of claim 17, wherein said generating comprises generating thepulse-width modulated control signal based on limiting the currentpassing through the power switch circuit to be at or below a definedinrush current.
 20. The method of claim 17, wherein said generatingcomprises dynamically adjusting one or more parameters of thepulse-width modulated control signal based on feedback indicative of anelectrical load on the robotic tool.
 21. The method of claim 17, whereinsaid generating comprises generating the pulse-width modulated controlsignal responsive to one or more first tool electrical signal modulepower control signals associated with the coupling of the first mastermodule and the first tool module.
 22. The method of claim 21, whereinthe one or more first tool electrical signal module power controlsignals comprise a control command to lock the first master module andthe first tool module, and a sensing signal that indicates whether allelectrical contacts between the first master module and the first toolmodule are engaged.
 23. The method of claim 17, further comprisingdirecting the power switch circuit to administer said pulsed applicationresponsive to the pulse-width modulated control signal.
 24. The methodof claim 14, wherein the applying of the one or more power supplies toboth the first master electrical signal module and the first toolelectrical signal module comprises applying the one or more powersupplies to the first master electrical signal module via a firstcircuit connected to the one or more power supplies and applying the oneor more power supplies to the first tool electrical signal module via asecond circuit connected to the one or more power supplies that iselectrically parallel to the first circuit, and wherein the step ofselectively suppressing application of the one or more power supplies tothe first tool electrical signal module, while maintaining applicationof the one or more power supplies to the first master electrical signalmodule, comprises selectively breaking or establishing the secondcircuit, while maintaining the first circuit.
 25. The method of claim14, wherein the applying of the one or more power supplies to the firsttool electrical signal module comprises passing electrical power betweenrobot-side electrical contacts of the first master electrical signalmodule and tool-side electrical contacts of the first tool electricalsignal module when the first master module and the first tool module arecoupled together, and wherein the method further comprises: preventingtransient electric arcs from forming across said robot-side and saidtool-side electrical contacts by suppressing application of the one ormore power supplies to the first tool electrical signal module duringthe coupling or uncoupling of the first master module and the first toolmodule; and enabling the coupling or uncoupling of the first mastermodule and the first tool module by maintaining application of the oneor more power supplies to the first master electrical signal module. 26.The method of claim 14, wherein the method is also for transferring therobotic tool between the robotic arm and a powered endpoint, bycoordinating coupling and uncoupling of the first tool module and thefirst master module with coupling and uncoupling of a second tool moduleconnected to the robotic tool and a second master module connected tothe powered endpoint, the method further comprising: applying the one ormore power supplies to both a second master electrical signal module,affixed to the second master module, and a second tool electrical signalmodule, affixed to the second tool module; and during the coupling oruncoupling of the second master module and the second tool module,selectively suppressing application of the one or more power supplies tothe second tool electrical signal module, while maintaining applicationof the one or more power supplies to the second master electrical signalmodule.
 27. A robotic tool changer system configured to removably attacha robotic tool to a first powered endpoint, comprising: a first toolmodule adapted to be connected to the robotic tool; a first mastermodule adapted to be connected to the powered endpoint, and toselectively couple to and uncouple from the first tool module; a firstmaster electrical signal module affixed to the first master module and afirst tool electrical signal module affixed to the first tool module,both adapted to be powered by application of the same one or more powersupplies; and a first power switch circuit configured to: selectivelysuppress application of the one or more power supplies to the first toolelectrical signal module, while maintaining application of the one ormore power supplies to the first master electrical signal module, duringthe coupling or uncoupling of the first master module and the first toolmodule; and upon coupling of the first master module and the first toolmodule, administer pulsed application of the one or more power suppliesto the first tool electrical signal module to transition fromsuppressing application to maintaining application of the one or morepower supplies to the first tool electrical signal module.
 28. Therobotic tool changer system of claim 27, wherein the first power switchcircuit is configured to administer said pulsed application responsiveto a pulse-width modulated control signal that is associated withcoupling of the first master module and the first tool module.
 29. Therobotic tool changer system of claim 28, wherein the pulse-widthmodulated control signal comprises an explicit control command thatindicates whether to turn power on or off to the first tool electricalsignal module.
 30. A method implemented by a robotic tool changer systemfor removably attaching a robotic tool to a first powered endpoint, byselectively coupling and uncoupling a first tool module connected to therobotic tool and a first master module connected to the poweredendpoint, the method comprising: applying the same one or more powersupplies to power both a master electrical signal module, affixed to themaster module, and a first tool electrical signal module, affixed to thetool module; during the coupling or uncoupling of the master module andthe tool module, a power switch circuit of the robotic tool changersystem selectively suppressing application of the one or more powersupplies to the tool electrical signal module, while maintainingapplication of the one or more power supplies to the master electricalsignal module; and upon coupling of the first master module and thefirst tool module, the power switch circuit administering pulsedapplication of the one or more power supplies to the first toolelectrical signal module to transition from suppressing application tomaintaining application of the one or more power supplies to the firsttool electrical signal module.
 31. The method of claim 30, wherein saidadministering comprises administering said pulsed application responsiveto a pulse-width modulated control signal that is associated withcoupling of the first master module and the first tool module.
 32. Themethod of claim 31, wherein the pulse-width modulated control signalcomprises an explicit control command that indicates whether to turnpower on or off to the first tool electrical signal module.